Jasmonates mediate responses to plant biotic- and abiotic-stress and influence plant development as well as secondary metabolism (for a recent review, see Avanci et al. 2010, GMR 9:484; Acosta and Farmer 2010, Arabidopsis Book PMC3244945. Today’s highlighted paper, at the moment in advanced view from Plant Physiology, sheds new light on the elusive mechanism behind the jasmonate inhibitory effect on plant organ development and growth, which has traditionally taken a back seat to its involvement in the stress response.
The authors used a range of traditional and systems-based methods to uncover the mechanism of growth inhibition by jasmonates (JA). First of all, they looked at the cell size and cell number in the first true leaves of Arabidopsis mutants altered in JA synthesis and perception, aos and coi1 respectively, in the presence and absence of methyl jasmonate (MeJA) treatment. Both cell size and cell number were reduced after treatment with MeJA in aos1 and the Col gl1 wildtype. This effect was minimal in coi-1, demonstrating the importance of COI1 in JA-mediated cell growth inhibition. Importantly, using flow cytometry they also showed that MeJA delays the switch from the mitotic cell cycle to the endoreduplication cycle, again in a COI1-dependent manner, as well as inhibiting mitotic cycle itself.
To work out the mechanism for JA’s effect on cell size, number, and ploidy, Noir, Bömer et al. performed novel global transcriptional profiling to identify the molecular players whose expression is regulated during leaf development by jasmonate via COI1. Senior author on the paper Alessandra Devoto from Royal Holloway, University of London explained, “Publicly available microarray studies conducted so far have been on whole seedlings and single timepoints, designed mainly to analyze the role of JAs in stress and defence. They are unsuitable to dissect the MeJA-dependent signalling underlying the physiological responses we have observed in planta. So we dissected MeJA dependent global transcriptional regulation during leaf development using the Arabidopsis ATH1 full genome DNA arrays.”
This analysis enabled the group to show, for the first time, that MeJA activates critical regulators of endoreduplication and differentially affects the expression of key determinants of DNA replication. They were also able to show that MeJA positively regulates the expression of S-phase genes, several of which encode pre-replication components.
Their discoveries also point toward a role for MeJA in the maintenance of a cellular ‘stand-by mode,’ as the expression of ribosomal genes was elevated throughout treatment with MeJA. Both Arabidopsis and N. benthamiana seedlings were able to recover when MeJA is removed, which also supports this hypothesis.
“The overall findings allowed us to propose a model for MeJA regulated COI1-dependent leaf growth inhibition, and most significantly to identify novel elements balancing MeJA regulated trade-off between growth ability and stress tolerance,” said Alessandra Devoto.
Highlighted paper and image credit: Sandra Noir, Moritz Bömer, Naoki Takahashi, Takashi Ishida, Tsui Tjir-Li, Virginia Balbi, Hugh Shanahan, Keiko Sugimoto and Alessandra Devoto (2013) Jasmonate controls leaf growth by repressing cell proliferation and the onset of endoreduplication while maintaining a potential stand-by mode. Plant Physiology Preview doi: http://dx.doi.org/10.1104/pp.113.214908
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